The present invention relates to a novel polyurethane composition and a method of preparing same.
Polyurethanes are used in many familiar products, such as elastomers, solid articles, films, and in the manufacturing of foams. The various uses require the polyurethanes to exhibit certain properties such as low temperature flexibility, high tensile strength, high tear strength, high elongation, abrasion resistance, solvent resistance and the like, to ensure that the articles made therefrom can withstand the environments in which they are used. The continuing and, indeed, growing attractiveness of using polyurethanes in various products and uses has prompted the continuing effort to identify polyurethanes exhibiting these properties to a greater degree, and exhibiting optimal combinations of these properties than currently available polyurethanes.
The present invention is directed to such polyurethanes. These are useful in the manufacture of foams, elastomers, solid articles such as shoe soles, and other uses to which polyurethanes are put.
Conventionally, polyurethanes are obtained by reacting a polyester polyol with a diisocyanate whereby the hydroxyl groups on the polyester polyol are endcapped with isocyanate groups, thereby forming a prepolymer. The prepolymer is chain extended by contacting it with a suitable di- or higher-functional chain extender bearing functional groups reactive with the terminal isocyanate groups on the prepolymer.
While some branched polyester polyols have found use in the manufacture of polyurethane, wherein the polyester is derived from a trifunctional or tetrafunctional polyol (such as, respectively, glycerin or pentaerythritol,) the present invention has unexpectedly discovered that polyesters derived from sorbitol provides superior properties compared to conventional polyurethanes.
The polyurethane of the present invention is prepared from a sorbitol-branched polyester. In a particular practice of the invention, sorbitol (or mixtures of sorbitol with other suitable polyols as hereinafter described) is synthetically incorporated into the backbone of a polyester. The sorbitol-branched polyester that results car be employed to fabricate polyurethanes by e.g., reaction with an isocyanacte with chain extension. The polyurethane that eventuates exhibits physical properties superior to those heretofore known, including improved low temperature flexibility, tensile strength, tear strength, modulus strength, elongation %, abrasion resistance, rebound %, solvent resistance etc.
The polyurethane of the invention is fabricated using a sorbitol-branched polyester. Without limitation, the sorbitol-branched polyester is formed by reacting sorbitol (or a mixture of sorbitol and other polyols as defined hereinbelow) and a diol with a diacid (or arhydride thereof).
As used herein:
Polyols: polyols useful in the present invention include those containing 2 or more (e.g. 5 to 12) hydroxyl groups and up to 50 carbon atoms. They may be in the D,L, or mixed D,L form. Alkoxylates of such polyols are also within the ambit of the present invention inasmuch as they are hydroxyl terminated. They can be alkoxylated with up to 30 moles (per mole of polyol) of alkylene oxide such as ethylene oxide, propylene oxide, butylene oxide etc. and mixtures thereof. Examples of polyols in this regard include: glcuose, dipentaerythritol, sucrose, tripentaerythritol, allitol, cyclodextrin (cycloheptaamylose), dulcitol (galactiol), glucitol, mannitol, altritol, iditol, ribitol, arabinitol, xylitol, maltitbl, lactitol, trimethylolpropane, glycerin, trimethylolethane, tris-(2-hydroxyethyl) isocyanurate, tris-(2-hydroxypropyl) isocyanurate, tris-(3-hydroxpropyl) isocyanurate triisopropanolamine, and pentaerythritol.
Diols: diols useful in the invention include those containing 2 to 12 carbon atoms. In cases where glycol ethers are utilized in the diol component, it is preferred that they contain from 4 to 12 carbon atoms. Examples of diols include: ethylene glycol, diethylene glycol (which is a preferred diol), 1,3-propylene glycol, 1,2-propylene glycol, 2,2-diethyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2,4-trimethyl-1,6-hexanediol, 2,4-dimethyl-2-ethylhexane-1,3-diol, 1,2-cyclohexanediol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, p-xylenediol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol.
Diacids: diacids useful in the present invention include: aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, aromatic dicarboxylic acids, ethylenically unsaturated alkenyl dicarboxylic acids, or mixtures of two or more of these acids. Preferred are alkyl dicarboxylic diacids which generally will contain 2 to 12 carbon atoms, and aromatic dicarboxylic diacids which generally contain 6 to 12 carbon atoms. Examples of useful diacids include: oxalic, malonic, dimethylmalonic, succinic, glutaric, adipic, trimethyladipic, pimelic, pivalic, dodecanedioc, 2,2-dimethylglutaric, azelaic, sebacic, maleic, fumaric, suberic, 1,3-cyclopentanedicarboxylic, 1,2-cyclohexanedicarboxylic, 1,3-cyclohexanedicarboxylic, 1,4-cyclohexanedicarboxylic, phthalic, terephthalic, isophthalic, tetrahydrophthalic, hexahydrophthalic, 2,6-norbornanedicarboxylic, 1,4-naphthalic, diphenic, 4,4xe2x80x2-oxydibenzoic, diglycolic, thiodipropionic, 4,4-sulfonyldibenzoic, and 2,5-naphthalenedicarboxylic acids. Anhydrides of any of the foregoing diacids are also employable.
Preferred diacids include: isophthalic acid, terephthalic acid, phthalic acid, adipic acid, tetrahydrophthalic acid, pivalic acid, dodecanedioic acid, sebacic acid, azelaic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, maleic acid, fumaric acid, succinic acid, 2,6-naphthalenedicarboxylic acid, glutaric acid, and any of the anhydrides thereof.
Formation of the Sorbitol-Branched Polyester:
In the present invention, the total amount sorbitol (or mixtures of sorbitol with other polyols) and diol is sufficient to provide an excess of hydroxyl groups with respect to diacid carboxylic groups (similar considerations apply to the use of anhydrides of said diacids). It will be recognized that to ensure that the sorbitol-branched polyester is capped with terminal hydroxyl groups, it may be necessary to provide in the reaction mixture more than simply a slight stoichiometric excess of the indicated component; the degree of excess is tempered, however, by the effect of excess on the distribution of polymeric chain lengths formed in the condensation polymerization.
Sorbitol is present in the reaction mixture in an amount sufficient to provide a residue in the resultant polyester constituting about 0.1 wt. % to about 15 wt. % of said polyester. In a preferred practice, this percentage is at least about 0.5 wt. %, more preferably at least about 1 wt %, including e.g., about 5% to about 15 wt %.
The reaction mixture containing the sorbitol, diol and diacid (or anhydride) is subjected to condensation polymerization conditions effective to cause the reactants to react with each other to form the sorbitol-branched polyester. In general, effective condensation polymerization conditions are familiar to (or otherwise readily ascertainable by) the practitioner. It is preferred not to carry out the reaction in a solution. However, if a solvent is desired, it should be high boiling (i.e. a boiling point above about 140xc2x0 C.) Examples of suitable solvents include: DMF (dimethylformamide), DMA (N,N-dimethylacetamide), xylene and DMSO. Combinations of solvents may also be employed.
Preferably, the reaction mixture for carrying out the condensation polymerization includes a small but effective amount (such as up to about 0.02 wt. %) of a catalyst for the polymerization. Useful catalytic compounds include: protonic acids, tin compounds, titanium compounds and antimony compounds.
Typical condensation polymerization conditions are provided by exposing the reactants to temperatures on the order of about 150xc2x0 C. to about 250xc2x0 C. As the reaction progresses, it is preferred to draw off water of condensation. A preferred method is to use nitrogen to purge the reaction mixture in order to remove the water.
The chain length (molecular weight) of the sorbitol-branched polyester produced can fall within a rather wide range; typically, a sorbitol-branched polyester will have a molecular weight in the range of about 200 to about 50,000. Amounts and identities of the reactants can be readily tailored to achieve desired molecular weight and distribution.
At the end of the condensation polymerization, the sorbitol-branched polyester can be recovered and separated from the reaction mixture.
Formation of the Polyurethane:
The sorbitol-branched polyester is reacted with one or more polyisocyanates, preferably one or more diisocyanates, optionally with one or more chain extenders, to produce the subject polyurethane.
Any organic polyisocyanate may be used in the process according to the invention. It is preferred to use polyisocyanates of the formula Q(NCO)2 wherein Q represents an aliphatic hydrocarbon group containing from 4 to 12 carbon atoms, a cycloaliphatic hydrocarbon group containing from 6 to 15 carbon atoms, an aromatic hydrocarbon group containing from 6 to 15 carbon atoms or an araliphatic hydrocarbon group containing from 7 to 15 carbon atoms. The most preferred diisocyanate is isophorone diisocyanate. Other preferred diisocyanates include: tetramethylene-diisocyanate, hexainethylene diisocyanate, dodecamethylene-diisocyanate, 1,4-diisocyanato-cyclohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane, 4,4xe2x80x2-diisocyanatodicyclohexylmethane, 4,4xe2x80x2-diisocyanatodicyclohexyl-propane-(2,2); 1,4-diisocyanato-benzene, toluene diisocyanates such as 2,4-diisocyanatotoluene and 2,6-diisocyanatotoluene; 4,4xe2x80x2-diphenylmethane diisocyanate, 4,4xe2x80x2-diisocyanatodiphenyl-propane-(2,2), p-xylylene-diisocyanate, a,a,axe2x80x2,axe2x80x2-tetramethyl-m or p-xylylene-diisocyanate and mixtures of these compounds. Mixtures of any of the foregoing can also be used. The mole ratio of polyisocyanate to sorbitol-branched polyester is generally stoichiometric, e.g. about 1:1 to about 30:1.
The reaction of the sorbitol-branched about polyester with the polyisocyanate can optionally be carried out in the presence of comonomer such as a lower diol containing 2 to 12 carbon-atoms or water. Typical amounts of such a comonomer are up to about 10 wt. % of the amount of all reactants present.
Reaction of the polyisocyanate and the sorbitol-branched polyester can be carried out at moderately elevated temperatures, e.g. about 50xc2x0 C. to about 150xc2x0 C. The reaction can be carried out with or without a solvent (inert). One preferred solvent is N-methyl pyrrolidone. Other suitable solvents include acetone, methyl ethyl ketone, toluene, dimethyl formamide, ethyl acetate, tetrahydrofuran, and dioxane.
As before stated, the reaction of the sorbitol-branched polyester and polyisocyanate may optionally include a suitable chain extender.
Satisfactory chain extenders include: water, diamines such as hydrazine, and alkyl and aromatic polyols, especially diols, and alkyl and aromatic diamines and triamines, wherein the alkyl moiety contains a total of 2 to 12 carbon atoms or the-aromatic moiety contains 6 to 10 carbon atoms. Other examples of chain extenders include: ethylene diamine, diethylene triamine, 1,2-diaminopropane, 1,3-diaminopropane, 1,4-diaminobutane, and 3,3,5-trimethyl-5-aminomethyl cyclohexylamine; and ethylene glycol, 1,2-dihydroxypropane, 1,6-dihydroxyhexane, and the polyols described herein as useful reactants to make the polyester.
In place of water (and combinations containing water) as a chain extender, a conventional foaming agent may optionally be used in forming the polyurethane product. A highly preferred foaming agent is carbon dioxide. Other foaming agents that may optionally be employed in the present invention include: methylene dichloride, CFC, and the like.